Conventional passenger carrying aircraft typically include an environment system for supplying air conditioned and pressurized air to the passenger compartment. This passenger air is typically provided from one or more gas turbine engines which power the aircraft in flight and must be clean and free from oil or fuel vapors or both to ensure passenger comfort and safety. A conventional gas turbine engine includes a compressor which pressurizes ambient air which is then mixed with fuel and ignited for generating combustion gases for powering the aircraft in flight. Conventional bleed systems exist for bleeding a portion of the pressurized air from the compressor and channeling it to the environmental system for providing the passengers with clean air.
Adequate amounts of clean air are typically provided at engine speeds greater than idle. However, at relatively low engine speeds such as at ground idle or descent idle, the pressure of the bleed air typically bled from available compressor mid-stages becomes unacceptably low for providing adequate clean air to the aircraft. Accordingly, conventional bleed systems typically also include a bleed port located in the vicinity of the compressor diffuser and combustion assembly which has the highest compressed air pressures in the engine. Since bleeding compressed air from the engine decreases engine propulsion efficiency, conventional bleed systems are configured for bleeding air at about only those pressures required for providing the passenger clean air at the various altitudes of aircraft operation and speeds of the aircraft engine. Bleeding air solely at the diffuser downstream of the last stage of the compressor wherein the compressed air has its highest pressures is not desirable for all operating conditions of the aircraft and engine since decreased operating efficiency will result, which, therefore, results in relatively complex bleed systems in a conventional aircraft.
Furthermore, when bleeding air in the vicinity of the diffuser and combustion assembly, the possibility of fuel vapors mixing with the bleed air channeled to the passenger compartment must be addressed and reduced or eliminated for ensuring passenger safety and comfort. Since the conventional fuel injectors channeling fuel to the engine's combustor, are an assembly of components including fittings, leakage of fuel may occur at various locations thereof. A suitable bleed system should reduce or eliminate the likelihood of any fuel leakage being carried with the bleed air to the passenger compartment.